High-power microwave discharge tube



I March 9, 1 948; SPENCER 2,437,579

' HIGH POWER MICRO-WAVE DISCHARGE TUBE Filed Sept. 23, 1942 3 Sheets-Sheet 1 .//w/v7'0,. .f PEECY L. SPENCER,

March 9, 1948. Q SPENCER 2,437,279

HIGH rowan MICRO-WAVE DISCHARGE TUBE Filed Sept. 25, 1942 3 Sheets-Sheet 2 //v v/v Toe; Pmcy L. 5Pf/VCEK,

March 1948'- P. L. SPENCER HIGH POWER MICRO-WAVE DISCHARGE TUBE Filed sebt. 23, 1942 5 Sheets-Sheet s //VVNTOR. FL' 'EC Y L. 5 5mm,

Patented Mar. 9, 1948 Percy L. Spencer, West Newton, Mass, assignor to Raytheon Manufacturing Company, Newton,

Mass, a corporation Application September 23, 1942, Serial No. 459,341

11 Claims. 1

This invention relates to an electrical space discharge tube of the magnetron type which is adapted to generate micro-waves of high power. This invention relates more particularly to such a tube in which the dimensions of the internal structure determine the frequency of theelectrical oscillations produced thereby.

Discharge tubes of the foregoing type have heretofore been constructed with a centrally disposed cathode surrounded by' the anode structure. Such an arrangement has imposeda practical limiton the total emitting area of the oathode and thus such tubes have been limited in the amount of current which they could be de signed to carry. The foregoing limitation has been particularly severe in the case of microwave oscillators producing wave lengths of the order of a few centimeters or less. In such cases the-space available for the cathode decreased in diameter as the wave length decreased so that cathodes of very limited emitting capacity necessarily had to be utilized in such tubes.

An object of this invention is to devisea discharge tube of the foregoing type with a novel configuration in which large cathode emitting. surfaces can be utilized and which are capable of carrying large values of load current and in which the size of the cathode may be substantially independent of the wave length of the oscillations generated by such a tube.

In discharge tubes. of the magnetron type in which a plurality of separate oscillating paths exist in the anode structure it is important that thenatural frequency of all such paths be made equal to each other.v Prior anode configurations for tubes of this .type have been very diflicult to construct so .as to obtain this equalitywith the result that in such tubes a certain amount of interference has existed between the various circuits which interference substantially reduced theefficiencyof operation of such tubes.

Another object ofthis invention is to produce a configuration having a plurality of separate oscillating pathswithin the electrode structure, which may be accurately and easily machined or otherwise fabricated-so that all said oscillating paths are of the same frequency.

Tubes of the foregoing type are often employed in systems where the deviceis called upon to produce pulses .of oscillations of relatively high intensity. Such pulsing operations have necessitated apparatus for thecontrol ofsubstantially all of the power fed to such device.

A nother object of this invention is to produce an arrangement in'wh-ich a grid electrode may a be utilized'to control the operation of the device,

tion of magnetron which possesses the advantages of ease of manufacture and assembly and which enables auxiliary electrodes to be utilized therein. 7

The foregoing and other objects of this invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings wherein:

Fig. 1 is an exploded perspective View of a discharge tube embodying my invention;

Fig. 2 is a perspective view partly in section of a magnet structure with which the tube of Fig. 1 may be utilized;

Fig. 3 is a cross-sectional view of the tube shown in Fig. 1 after said tube has been assembled, the section of Fig. 3 being taken along line 3-3 of Fig. 4;

Fig. 4 is a cross-sectional view of the tube taken along the line 4-4 of Fig. 3;

Fig. 5 is a cross-sectional detail of the mounting of the oscillation pick-up loop; and

Fig. 6 is a fragmentary cross-sectional view of the tube taken along line 66 of Fig. 4.

The tube as illustrated in the drawings consists of an anode structure I which is formed of a suitable conducting material, such as highconductivity copper, and a cathode structure 2. If desireda grid electrode 3 may be interposed between the anode l and the cathode 2 in order to provide for control of the discharge between said electrodes. The cathode structure 2 is in the form of a hollow flat annular shaped ring of which the lower surface is adapted to be the active electron emitting surface. Preferably, therefore, a heat shield 4 is adapted to be placed over the upper surfaces of the cathode 2 in order to prevent excess loss of heat from the non-emitting surfaces of the cathode.

The foregoing elements are adapted to be mounted in a casing consisting of an outer sleeve 5, an inner sleeve 6, and end caps 'l and 8- which engage the outer ends of the sleeves 5 and 6 and close off the annular space formed between said sleeves. Each of the elements 5, 6, l and 8 may likewise be formed of suitable conducting material, such as, copper. 'If desired, the end cap I may be formed integrally with the anode I, or said elements may be formed separately and then fastened together as by being brazed to each other 3 with silver solder. The end cap 8 is adapted to carry the cathode 2, the grid 3, and the cathode heat shield 4, all of which may be assembled on said end cap 8 prior to their assembly with the rest of the tube structure.

The anode is formed from an annular block of metal containing a central bore 3. A plurality of radial slots l6 are cut from one end of the annular block and are of a predetermined depth less than the total length of said block thus leaving a solid end ring portion As stated above this anode structure may be integral with or otherwise fastened to the lower end cap I. The cap "I extends beyond the outside boundary of the anode and is provided with a stepped outer edge |2 adapted to fit into the lower end of outer sleeve.

5 which is correspondingly stepped. The cap I likewise extends inwardly beyond the innerwalls of the bore 9 and is provided with an inner stepped edge i3, also adapted to fit onto the lower end of the inner sleeve 6 which is correspondingly stepped. In order to lead off the oscillations which are generated in thetube, there is provided a coupling loop I l which is placed in one of the slots H! with its plane transverse to said slot. The coupling loop i4 is carried by a pipe l5 which is hermetically sealed in an opening extending through the cap 1 and the end ring portion ll of the anode One end of the coupling loop 54 is directly connected to the inner end of the pipe I5 as shown most clearly in Fig. 5. The other end of the coupling loop i4 is connected to a lead wire |6 which passes through a glass seal sealed tothe outer end of the pipe-l5. An outer pipe I505 may be screw threaded onto the outer surface of the pipe Elite form with the conductor it a concentric line through which the oscillations may be conducted to a suitable utilization device.

The cathode 2 is formed of a hollow toroidal member N3 of a suitable conducting material, such as nickel. This member iscoated on its lower face with suitable electron emissive materials, such as the alkaline earth oxides. It will be seen that in this way a relatively extensive electron emitting area is provided. The emitting area of the cathode is heated by a coiled heater ill of refractory material, such as tungsten or the like. The coil of the heater l9 may be likewise bent into the proper toroidal shape to fit within the hollow interior of the member l8. A suitable form of the coil heater l9 may be a closed spiral, to which is connected, at two diametrically opposed points, a pair of lead-in wires 28, 2| for supplying heating current to the coil i9. Preferably the coil I9 is coated with an insulation coating so as to prevent short-circuiting thereof by the member 8. The lead-in conductors 2i] and 2| pass through openings provided in the upper surface of the member E8. The conductor 21! is insulated from the member i8 by a stepped insulator 22 which is mounted within the opening through which the lead wire 2% passes. The conductor 2 I, however, is electrically connected to the member l8 and thus may serve as a lead for the cathode discharge current as well as one of the heater leads; The cathode structure is supported by the conductors 20 and 2| irom'a pair of glass seals 23 and 24 sealed to the outer ends of a pair of conducting pipes 25 and 2 5 hermetically sealed in openings extending through the upper end cap 8. 7

As previously stated a light metal heat shield 4 may be utilized to prevent excessive heat losses from the back portion of the cathode. Conductors and 2| thus likewise pass through openings in the heat shield 4. In order to prevent short-circuiting of the heater coil l9, the stepped insulator 22 also extends into the opening in the shield 4 through which the conductor 20 extends. The heat shield 4 is preferably spaced a short distance from the back surface of the member E8. The outer step in the insulator 22 provides the proper spacing for one side of the heat shield 4. The other side of the shield 4 may be spaced by a conducting washer 28 of the proper thickness which may be welded to the members l8 and 2!. The heat shield may be retained firmly in place by an outer conducting washer ZS-Iikewise welded to the conductor 2| and to th member 4. By the foregoing construction the shield 4 is electrically connected to the oathode-and maintained at the cathode potential.

Although most tubes of the foregoing type operate without the interposition of a grid electrode between the. catho e. and the anode, if desired such a grid electrode 3 may be utilized in the present construction. The grid electrode 3 may b formed of a mesh material preferably with an end binding of metal so as to strengthen it. The grid electrode is likewise formed as a flat washer and may be supported by a pair of leadin conductors 30 and 3|. These lead-in conductors preferably lie in a plane at right angles to the plane containing the lead-in wires 20 and 2|. The lead-in conductors 3i) and 3| are insulat-ed from the cathode 2 by. passing through openings in the upper and lower surfaces of the member, illand through corresponding openings in the heat shield 4.. If necessary, insulators might be inserted in such openings so as to insure against electrical contact between the conductors 3i! and 3| and any of the cathode structure, The conductors 30 and 3| likewise pass between turns of the coiled heater |9. If necessary the coils may be spread so as to provide for such passage. In any event since the coil H] is coated with insulation the danger of contact with g the conductors 3|] and 3| is substantially eliminated, The conductors 3i] and 3| are supported by glass seals 32 and 33 sealed to the outer ends of pipes 34 and 35 likewise hermetically sealed in openings extending through the top end cap 8.

In order to assemble the tube construction, the anode and coupling loop M are mounted on the lower end cap 1. Likewise the members 2, 3 and i are mounted on the upper end cap 8. As described in connection with the lower end cap I, the upper end cap 8 is likewise provided with outer and inner stepped edges which fit on the correspondingly stepped edges of the sleeves 5 and 6. The end caps 1 and 8 carrying their associated members are then inserted onto the lower and upper ends respectively of the sleeves 5 and 5. All joints are then hermetically sealed as by brazing with a silver solder. I have found that this is a very effective way of producing a completely hermetically sealed structure.

The tube as assembled above may then be exhausted in the usual manner through an exhaust tube, such as 32a, provided on one of the glass seals 32. After the tube is degasified and exhausted, the exhaust tube 32a is sealed off in accordance with the well known practice.

31 and a surrounding annular pole piece 38, thus 5.. prcyidingeans. 81111111512585}???MI'OSSWWhiCh-Eiifflidifl] magnetic:linesofwforce-rare:adaptedit pass. ;-.-The annular-pole piece 38. is .mountedat-the cuter end ofi-aqcyl-indrical. side casing 39F which-is provided withiaifiat-bottom wall 40. eIn:thecentenofithe theslowen wall-4| to-iettherpi-pealfi pass through.

The.- magnet 3 5 may be. formed .as'ra permanent magnet-serif desired :amenergizlngi-coil.-,-such:as indicatedeat .5 31in Eig; 3rma'y; be utilized :to' supply the tmagnetomotiye :force: necessary to create the magnetic-flux.

For those operations xin's-whichsit is desired'ato have the grid electrode control :pulsing Operations of: the tube, the'apositi-omofvtha :tube'zissadj usted so thatthe .tcp. edgesoi thermagnetic poles 31' and 548 die :justbelow theilowerwsurfaeeiofi the.

grideelectrcde 3. irIn-this way' thewmagneticzfiel'd is substantially limited torthe region adjacent-the anode electron. receiving surfaces; sand the: grid electroded .is-located sin'sausubstantially: magnetic field free (space. Ofcourse. it::is :to be understood:

that-.thespacing. between. thezelectrodesuandathe various other spacial :nelaticnships;arezillnstrated merelydiagrammaticallydn the drawings. "..Thus, if necessary the; spacings? =coul'di.: be: greatly. 11increased Zlfirequiredjitd=provide the proper magnetic field substantially limited to the region ad jacent the electron receiving-surfaces of the anode, and .to. provide.v a. substantial -m-agnetic field free space in which the grid-is ..to.be-placed. With such an arrangement the electrons emitted from the cathode are"under-completecontrol of the grid-before being subjected to the magnetic field. :Thus; for example, thengrid electrode 3 could modulate electron flowzeand in thist way modulate-.theoscillations generated. Where-pulsingeis desired, the proper potential couldtibe impressed ion-the grid 3 at thesproper,time'interyals to completely cut off the electronflow or to permit it to pass; thus'pro'ducing pulses of oscillations-separated by the proper:-time intervals.

When: the various elements :cfsthe tubeareenergized withltheproper-potentials; electrons are emitted frornsthe lowerlfacez ofF-the member 1 8. The). electrons .so emitted '-.;are attracted toward the anode by the positive potential impressed hereon and in so doing come under the influence of the magnetic field existing in the inter-electrode space. Thus, for example, a particular electron may be attracted toward one of the anode segments formed between two slots ID. The magnetic field, however, being transverse to the electrostatic field deflects the electron in a curvilinear path at right angles to the fields. Thus, said electron, instead of reaching the anode segment which accelerated it, falls on an adjacent segment of the anode. This action feeds energy to said adjacent segment and causes oscillations to be generated within the anode structure. This action, of course, is the well known operation which exists in magnetrons of the multiple anode type. Each pair of adjacent anode segments together with the portion of the ring ii joining them form a circuit containing inductance and capacitance. This constitutes a tuned oscillating circuit whose frequency is determined byisaidzinductance andacapacitance. .z-z-All, oithese circuits=-.-which :exist. in ithe anode:structure are electrically:connected. 3 This. is due to, the. fact that: each: segment forms an integral part i of two adjacent:oscillatingcircuits. Thus, if all of these circuitssare tunedvto' the samecfrequency, they willrreinforce: each "other and "the entire :tube will generate.:oscillationsof relatively-high, power whichmay be.;led;by:the lead 1 6. and the pipe lea to: any; suitable. utilization. device.

. the frequency of 'eachaof the oscillating circuits.

,Qf conrseit istoibe. understoodithat'this invention is not limited to the details oi..construction asadescrihed. abovezinasmuch asmany equivalents will suggest themselves toithoseiskilled in thez art.

1 What is claimed is:

- electrical space: discharge devicev comprisinga ;cathode;' an.=anode, said anode having a plurality ofsections having electron receiving surfaces zidisposed. substantially in a plane, said surfaces; beingspaced :from .each other, said cathode? having an electronaemitting surface. disposed substantially .in: a:.plane substantially parallel :to the planeiofssaid:felectron receiving surfaces, and means adjacent the.- discharge; path-betweenxsaid 40 planes forsproducingi a: magnetic .field transverse to isaididischargeipath 1'. 2;:An-nelectrica1 space discharge ?device comprisingsa cathode, an anode, said anodethaving arelatively extended. side disposed substantially ina .plane;.rsacidranode having a plurality of slots extending from saidside at an angle to said plane,

said cathode having, an electron-emitting surface disposed substantially -in;.a plane substantially parallelto the; plane :of saidzanode side, and

, means: adjacent:.thedischargepath between said planes f or; producing. a: magnetic field transverse to? said discharge 1 path.

3. 'An:--xeleictrical :spacex discharge device comprising.amathodeand'ananode, said anode being an annular shaped conductor having one end disposed substantially in a plane, said anode having a plurality of slots extending from said end at an angle to said plane, the surfaces of said end of said anode between said slots forming electronreceiving surfaces, said cathode having an electron emitting surface disposed substantially in a plane substantially parallel to the plane of said anode end.

4. An electrical space discharge device comprising a cathode and an anode, said anode being an annular shaped conductor having one end disposed substantially in a plane, said anode having a plurality of radially disposed slots extending from said end at an angle to said plane, the surfaces of said anode between said slots forming electron-receiving surfaces, said cathode having an electron emitting surface disposed substantially in a plane substantially parallel to the plane of said anode end.

5. An electrical space discharge device com-'- prising a cathode, an anode, said anode being an annular shaped conductor having one end disposed substantially in a plane, said anode having a plurality of slots extending from said end at an angle to said plane, the surfaces of said anode between said slots forming electron-receiving surfaces, said cathode having an electron emitting surface disposed substantially in a plane substantially parallel to the plane of said anode end,

and means adjacent the discharge path between said planes for producing a magnetic field transverse to said discharge path.

6. An electrical space discharge device comprising a cathode, an anode, said anode being an annular shaped conductor having one end disposedsubstantially in a plane, said anode having a plurality of slots extending from said end at an angle to said plane, the surfaces of said anode between said slots forming electron-receiving surfaces, said cathode having an annular shaped electron emitting surface disposedin a plane substantially parallel to the plane of said anode end, and means adjacent the discharge path between said planes for producing an annular magnetic field extending radially and transverse to said discharge path.

'7. An electrical space discharge device comprising a cathode, an anode, said anode having a' surfaces disposed substantially in a plane, said surfaces being spaced from each other, said cathode having an electron emitting surface disposed substantially in a plane substantially parallel to the plane of said electron receiving surfaces, means adjacent the discharge path between said planes for producing a magnetic field transverse to said discharge path, said magnetic field being limited substantially to a space adjacent said'anode, and a control grid disposed in the space between said two planes which is substantially magnetic field free.

10. An electrical space discharge device comprising a cathode, an anode incorporating a plurality of cavity resonators, said anode including a plurality of sections providing a plurality of spaced electron receiving surfaces all of which are disposed in a single plane, and said cathode having an electron emitting surface disposed in a plane parallel to the plane of said electron receiving surfaces, and a control grid disposed between said two planes.

11. An electrical space discharge device comprising an anode incorporating a plurality of cavity resonators, said anode including a plurality of sections providing a discontinuous annular electron receiving surface, a cathode, spaced from said anode, and having an electron emitting surface parallel to the electron receiving surface of said anode, an auxiliary electrode disposed adjacent said anode and said cathode, and means adjacent the discharge path between said anode 8. An electrical space discharge'device comnetic field being limited substantially to a space adjacent said anode, and a control grid disposed in the space between said cathode and anode which is substantially magnetic field free.

9. An electrical space discharge device comprising a cathode, an anode, said anode having a plurality of sections having electron receiving and said cathode for producing a magnetic field transverse to said discharge path.

PERCY L. SPENCER.

REFERENCES CITED The following references are of record in the file of this patentu Certificate of Correction Patent N 0. 2,437,279.- March 9, 1948i PERCY L. SPENCER It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 5, line 56, for the word I hereon read thereon; column 7, line 42, claim 8, for said second occurrence read each; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 4th day of May, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommzaszaner of Patents. 

